Differential drive for a superimposed steering system

ABSTRACT

An overriding drive for an overriding steering system, wherein a steering angle inputted by the driver can be overridden by another angle by a control according to correcting variables and the transmission ratio can be modified, and which is characterized in that the overriding drive is locked electromechanically in dependence on further correcting variables representative of an operating state of the vehicle.

TECHNICAL FIELD

The present invention relates to a locking device and an overridingdrive for an overriding steering system, wherein a steering angleinputted by the driver can be overridden by another angle by means of acontrol according to correcting variables.

BACKGROUND OF THE INVENTION

Up-to-date motor vehicles, in particular passenger vehicles, aregenerally equipped with hydraulic or electrohydraulic servo steeringsystems, wherein a steering wheel is forcibly coupled mechanically tothe steerable vehicle wheels. The power assistance is so configured thatactuators, e.g. hydraulic cylinders, are arranged in the mid-area of thesteering mechanism. A force generated by means of the actuators assiststhe actuation of the steering mechanism in response to the rotation ofthe steering wheel. This arrangement reduces the force the driver has toexert during the steering maneuver.

Overriding steering systems are disclosed in DE 101 59 800 A1 and DE 10159 700 A1, the contents of which are part of the application and onwhich the application is based. Said overriding steering systems arecharacterized in that it is possible for an actuator to superimposeanother angle, if required, on the steering angle inputted by thedriver. The additional angle is defined by a controller and used toenhance the stability and agility of the vehicle. It is also feasible tocompensate disturbances and to realize the gradient wheel steering angleby way of the steering wheel angle as a function of the driving speed ofthe vehicle. Hydraulic or electric actuators are used.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to provide an overriding drive or alocking device, wherein the driver can apply a steering angle to thewheels of the vehicle when the electronics or the energy supply fails.

According to the invention, this object is achieved in that theoverriding drive is locked electromechanically in dependence on furthercorrecting variables representative of an operating state of thevehicle. In the overriding drive, a superposition with another angleallows additionally or simultaneously changing the transmission ratio ina favorable way. The overriding drive of the overriding steering systemaccording to the invention in particular enables a safe and comfortableoperation.

It is advantageous that quantities such as ignition on/off, enginerotational speed and like factors are monitored to detect the operatingstate, and that the quantities are analyzed for detecting whether theengine is or is not switched off or an energy supply is or is notsafeguarded, respectively. The plausibility of the motor's position andof the sensor signals is monitored to enhance the reliability inoperation.

In a favorable embodiment, the overriding drive includes a freewheelingmechanism, which is lockable in operative and/or positive engagement.

The activation of the locking is preferably switchable and, in anespecially preferred fashion, it takes place simultaneously for theoperative and positive locking.

In another favorable design, the operative locking is provided by atleast one first clamping member, preferably by three to nine clampingmembers, being brought into frictional contact with an inner ring of thefreewheeling mechanism by way of a radial actuation, while the positivelocking is provided by at least one second clamping member, preferablyby three to nine clamping members, being brought into a form-fit contactwith the inner ring of the freewheeling mechanism by way of a radialactuation.

In addition, it is favorable that a first actuating ring is associatedwith the freewheeling mechanism for the positive connection and a secondactuating ring is associated therewith for the frictional connection,said rings being entrained with the clamping members upon radialactuation thereof so that rotation of the inner ring is prevented bymeans of a clamping contour at an outer ring of the freewheelingmechanism. Favorably, a defined angle, i.e. twisting angle, is alloweddue to the frictional connection before a positive connection develops.

The object of the invention is also achieved by way of a locking devicethat is preferably provided for an overriding drive of the typedescribed hereinabove and characterized by the provision of afreewheeling mechanism, which is operatively and/or positively lockable.

The activation of the locking is preferably switchable and, in anespecially preferred fashion, it takes place simultaneously for theoperative and positive locking.

In a favorable design, the operative locking is provided by at least onefirst clamping member, preferably by three to nine clamping members,being brought into frictional contact with an inner ring of thefreewheeling mechanism by way of a radial actuation, while the positivelocking is provided by at least one second clamping member, preferablyby three to nine clamping members, being brought into a form-fit contactwith the inner ring of the freewheeling mechanism by way of a radialactuation.

Preferably, the first clamping member is elastically arranged andpermits a defined angle, i.e. twisting angle.

It is arranged for by the invention that a first actuating ring isassociated with the freewheeling mechanism for the operative orfrictional connection and a second actuating ring is associatedtherewith for the positive connection, said rings being entrained withthe clamping members upon radial actuation thereof so that rotation ofthe inner ring is prevented by means of a clamping contour at an outerring of the freewheeling mechanism.

Advantageously, it is provided that locking is effected by anelectromechanical transducer that includes a first actuating element forthe operative or frictional connection and a second actuating elementfor the positive connection, said actuating elements acting on theclamping members and being moved by an electromagnetically operablearmature in opposition to a spring force for the purpose of locking orunlocking the freewheeling mechanism. This design according to theinvention renders it possible to safely fix or lock an element thatshall be locked by using very low adjusting and retaining forces and,thus, only low (electrical) energy. The result is that only a smallmounting space is required.

According to the invention, the freewheeling mechanism has a steppedcontour so that the inner ring is initially retained by means of africtional connection.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is a schematic general overview of the overriding steering systemof the invention.

FIG. 2 is a schematic view of a planetary gear with a freewheelingmechanism and a locking device according to the invention.

FIG. 3 is a view of the freewheeling mechanism with locking device.

FIG. 4 is a perspective view of the freewheeling mechanism.

FIG. 5 is a top view of a section of the freewheeling mechanism withlocking device.

FIG. 6 is a first section of the freewheeling mechanism with lockingdevice.

FIG. 7 is a second section of the freewheeling mechanism with lockingdevice.

FIG. 8 is a side view of a section of the freewheeling mechanism.

FIG. 9 is a section of the freewheeling mechanism with locking device inthe de-energized condition.

FIG. 10 is a section of the freewheeling mechanism with locking devicein the energized condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The overriding steering system shown in FIG. 1 includes a hand steeringwheel 50 that is connected to a steering rod 53 by way of a steeringcolumn 51, into which an overriding drive 6 is inserted, and by way of asteering gear 52. Displacement of the steering rod 53 permits turning ofthe wheels 54, 55. Turning of the wheels 54, 55 is assisted by means ofa hydraulic unit 56 and by a corresponding control of the hydraulicpressure by means of a valve unit 57. A pump 58 generates the pressure.

The function of an overriding drive 6 in the overriding steering systemshown in FIG. 1 involves adjusting an overriding angle 12 irrespectiveof the driver through a control by means of correcting variables whichcan be produced e.g. by a driving dynamics system (ESP controller). Tothis end, a planetary gearing with two sun wheels and three step planetpinions as described in DE 101 59 8000 A1 or DE 101 59 700 A1 is used.The step planet pinions are mounted in a satellite carrier (cage) .However, the invention is expressly not limited to a planetary gearingas overriding drive 6. Thus, all other pick-off gears known in the artmay be used as well.

The transmission ratio of the vehicle steering system is composed of thetransmission ratio of the steering gear and the overriding drive. Wherethe objective is to modify the transmission ratio to a definedtransmission ratio, it is necessary to additionally drive a component ofthe overriding drive. Said driving is carried out by way of an electricmotor (E-Motor) 8, whereby the variation of the transmission ratio ispossible in a wide range.

The motor 8 can be coupled to the gear 6, thus, to the planet cage inthe case of a planetary gearing, by means of a self-locking gear (wormgear or helical gear) or a non self-locking gear (drawing means gearingor toothed gearing) Preferably, however, a drawing means gearing, inparticular a belt drive, is used.

To realize a fixed transmission ratio in operating states when the motor8 is switched off, it is absolutely necessary to fix the overridingdrive 6. To this end, the cage is prevented from turning in a planetarygearing. This is possible by means of locking of the gear components tobe locked, meaning the cage in a planetary gearing, e.g. in relation toa stationary housing, while a first gear shaft (gear input shaft) 7 isdirectly connected to a second gear shaft (gear output shaft) 9 bytransmission means, especially through the planets of the gear. It isprovided in the invention that the cage of the planetary gearing ispositively and operatively lockable in dependence on the operatingstates.

FIG. 2 schematically shows the locking device with a freewheelingmechanism and a planetary gearing as an overriding drive in more detail.

The locking device 1 includes an electromechanical actuating unit 3 anda positive and operative freewheeling mechanism 2. The locking device 1is coupled positively to the gear housing 5 by way of a clutch 13.Preferably, the locking device 1 is herein used in an electromechanicaloverriding steering system (ESAS) (4) for motor vehicles. Other rangesof application with similar safety-relevant requirements are alsofeasible for the locking device 1.

In the above-mentioned application, the gear housing 5 of the overridingdrive 6 is locked by way of the locking device 1 in the non-activatedcondition or in the case of a fault. Thus, a throughgrip of the two gearshafts 7, 9 is effected by way of the planetary gearing 10 with atransmission ratio iG 11 in a range of roughly 1:1.0 to roughly 1:1.2,preferably 1:1.1 or 1:1.2. The overriding steering angle 12 is lockedthen.

The freewheeling mechanism 2 and the adjacent components of the lockingdevice 1 are illustrated in FIGS. 3 to 8 in more detail. The lockingdevice 1 of the invention is a functionally relevant component. In thede-energized condition of the electromechanical actuating unit 3, thefreewheeling mechanism 2 is locked by way of the one operativelyconnected freewheeling mechanism 14 and a positively connectedfreewheeling mechanism 15.

Said freewheeling mechanism 2 generally includes an outer ring 16, anactuation throughgrip 17, an immovable bearing 18, a movable bearing 19,a clamping member 20 for a frictional connection, a clamping member 21for a positive connection, an actuating ring 22 for the frictionalconnection, an actuating ring 23 for the positive connection, a springelement 24, and an inner ring 25.

When the clamping members 20, 21 are actuated radially by means of anactuating force 26 in opposition to the spring force 27 induced by thespring elements 24, the clamping members 20, 21 will get into contactwith the rotating or immovable inner ring 25 in frictional and positiveconnection (see FIGS. 6 and 7). The frictional and positive connectioncauses entrainment of the two actuating rings 22, 23 by way of thespring force 27 and the positive connection 28 and operative connectionwith the clamping members 20, 21. The result is that the clampingmembers 20, 21 are clamped between the outer ring 16 and the inner ring25 by means of the clamping contour 29 provided in the outer ring 16,and block further rotation 30 of the inner ring 25 on both sides.

When the actuating force 26 is released again, the acting spring force27 will produce a restoring torque 31 at the actuating rings 21, 22, andthe clamping members 20, 21 are reset to their zero position 32 when therotation 30 is reversed. The resetting torque of the actuating rings 22,23 produced by the spring elements 24 is increased in the zero position32 due to a special contour 33 of the clamping contour 29. Theembodiment illustrated in FIGS. 2 to 8 provides a high degree offunctionality of the freewheeling mechanism 2 and ensures safe unlockingin the non-actuated condition. The actuating unit 3 of the lockingdevice 1 is shown in detail in FIGS. 9 and 10. The purpose of said unitis to ensure safe locking of the freewheeling mechanism 2 by means of apositive and frictional connection. The actuating unit 3 issubstantially composed of an electromechanical transducer 34, anarmature 35, an actuating element 36 for a frictional connection, anactuating element 37 for a positive connection, a compression spring 38,and an armature spring 39.

In the energized condition (see FIG. 10), the armature 35 is attractedby means of the electromechanical transducer 34 in opposition to anintegrated spring element 39 and maintains the two actuating elements36, 37 in their unlocking position 41 by means of an integrated stop 40.Both freewheeling mechanisms 14, 15 adopt their unlocked position. Thisallows free rotation of the inner ring 25. The armature 35 is notpositively connected to the electromechanical transducer 34 and isattracted and retained alone by way of electromagnetic air slot forces42. When the electromechanical transducer is separated from the housing43 for mechanical reasons, the non-mechanical coupling to the armature35 will cause the armature to instantaneously lock the freewheelingmechanism 2 by means of the armature spring 39.

When the current at the electromechanical transducer 34 drops, thearmature spring 39 integrated at the armature 35 will urge the armature35 downwards into the locking position 44 (see FIG. 9). The actuatingforces 26 acting will activate both freewheeling mechanisms 14, 15 tolock the inner ring 25 of the freewheeling mechanism 2. Due to a steppeddiameter 45 of the positive and frictional connection 14, 15, thefreewheeling mechanism 2 is so configured that the frictional connection14 will initially lock the inner ring 25. When the frictional connectionis creeping, the actuating element of the positive connection 37 loadedby the compression spring 38 will push the clamping member 21 and safelylock the positively connected freewheeling mechanism 15. Safety isoptimized in that there is no mechanical coupling between theelectromechanical transducer 34 and the armature 35.

Thus, safe locking is ensured in every situation by means of theintegration of a positively and operatively connected freewheelingmechanism 14, 15 of the invention, effecting a high degree ofoperational safety of the electromechanical actuating unit 3, while thepositive connection is favorably used to ‘slow down’ the planet cage.

1. Overriding drive for an overriding steering system, wherein asteering angle inputted by the driver can be overridden by another angleby means of a control according to correcting variables, and wherein theoverriding drive is locked electromechanically in dependence on furthercorrecting variables representative of an operating state of thevehicle, the overriding drive including a freewheeling mechanism havingan inner ring, which inner ring is configured to be locked in bothoperative engagement by at least a first clamping member and positiveengagement with a second clamping member, wherein the operative lockingis provided by the at least one first clamping member, being broughtinto frictional contact with the inner ring of the freewheelingmechanism by way of a radial actuation, and the positive locking isprovided by the at least one second clamping member, being brought intoa form-fit contact with the inner ring of the freewheeling mechanism byway of a radial actuation and wherein a first actuating ring isassociated with the freewheeling mechanism for the positive connectionand a second actuating ring is associated therewith for the operativeconnection, said rings being entrained with the clamping members uponradial actuation thereof so that rotation of the inner ring is preventedby means of a clamping contour at an outer ring of the freewheelingmechanism.
 2. Locking device, which includes a freewheeling mechanismthat has an inner ring that is both operatively and positively lockableby distinct clamping members, wherein the operative locking is providedby at least one first clamping member, being brought into frictionalcontact with the inner ring of the freewheeling mechanism by way of aradial actuation, and the positive locking is provided by at least onesecond clamping member, being brought into a form-fit contact with theinner ring of the freewheeling mechanism by way of a radial actuationand wherein a first actuating ring is associated with the freewheelingmechanism for the operative connection and a second actuating ring isassociated therewith for the positive connection, said rings beingentrained with the clamping members upon radial actuation thereof sothat rotation of the inner ring is prevented by means of a clampingcontour at an outer ring of the freewheeling mechanism.
 3. Lockingdevice as claimed in claim 2, wherein the freewheeling mechanism has astepped contour so that the inner ring of the freewheeling mechanism isinitially retained by means of a frictional connection.
 4. Lockingdevice, which includes a freewheeling mechanism that has an inner ringthat is both operatively and positively lockable by distinct clampingmembers, wherein the operative locking is provided by at least one firstclamping member, being brought into frictional contact with the innerring of the freewheeling mechanism by way of a radial actuation, and thepositive locking is provided by at least one second clamping member,being brought into a form-fit contact with the inner ring of thefreewheeling mechanism by way of a radial actuation and wherein lockingis effected by an electromechanical transducer that includes a firstactuating element for the operative connection and a second actuatingelement for the positive connection, said actuating elements acting onthe clamping members and being moved by an electromagnetically operablearmature in opposition to a spring force for the purpose of locking orunlocking the freewheeling mechanism, respectively.